1. Field of the Invention
The present invention relates to a method of producing algae cultivating medium for cultivating algae on a large scale in seas and lakes. In particular the present invention relates to a method of producing nutriment supply medium for cultivating algae through the effective use of coal ashes or incineration ashes generated from thermal power plants or incinerators, or sands or crushed shells.
2. Description of the Related Art
Microscopic algae having high sunlight utilization ratio per unit area show high CO2 fixation ability compared with plants on land. Accordingly, cultivating algae is regarded as a promising procedure for fixing CO2 in the air. For this reason, there have been studies for utilizing microscopic algae absorbing and fixing CO2 studies as a method of preventing the global warming up, in addition to some development works for producing useful products such as substitute fuel for oil from the cultivated algae.
Studies for cultivating microscopic algae in a photo-reactor have been performed in many research laboratories where exhaust gas rich in CO2 is carried from a thermal power plant to the photo-reactor in which sunlight can be efficiently irradiated by concentrating the light.
In order to fix so much amount of CO2 as a level quantity contributing to prevent the global warming by cultivating algae, it is required to cultivate the algae in a huge area. According to a trial calculation, cultivating algae in an area of a square having a side of about 300 km is necessary to fix 10% of CO2 generated in Japan.
Since such a huge area is not available in an inland area in Japan, a large-scale cultivating is limited to carry out in the oceans. In the oceans, however, an efficient supply of nutriments has been difficult. When nutriments for the algae are sprayed in the oceans, the nutriments rapidly spread out in the oceans. Accordingly, almost all of the nutriments are not used for cultivating the algae but induce eutrophication and contamination of the entire oceans.
Accordingly, a medium which fixes the nutrients at the surface of the oceans and supplies the nutrients in accordance with the increase of the algae. Some of the present inventors submitted a patent application (Japanese Patent Application No. 10-52050) relating to manufacture of a medium capable of floating on water and supplying the nutriment. The application is a result of widely studying the way for supplying nutrient to the algae in the ocean.
The manufacturing of the medium that can supply the nutriment to cultivate the algae in the oceans or the like became possible as a result of the invention described above. The medium described in the patent application (Japanese Patent Application No. 10-52050), however, contains water repellent in an appreciable quantity to have floating ability in water. The water repellent is the most expensive among the raw materials of the medium. In addition, the water repelling ability of the medium gradually deteriorates, and the medium become unable to float in water when the medium is kept floating over long period.
The present invention is carried out to solve the problem described above. An object of the present invention is to provide a method for manufacturing inexpensively a large quantity of algae cultivating medium that floats in water and works as nuclei for cultivating the algae. Industrial waste such as coal ashes from thermal power plants, incineration ashes, sands, crushed shells or the like is utilized as raw materials of the medium. The volume produced algae cultivating medium by the method can cleanly cultivate the algae by dispersing in a huge ocean area.
The method of manufacturing an algae cultivating medium in the present invention comprises the steps of mixing raw material including an inorganic material, a curing material, and an algae cultivating nutriment to form a mixture, molding the mixture into a molded body, and curing the molded body. These steps are carried out so that the algae cultivating medium is water floatable.
In the present invention, the molded body is preferably manufactured so that the density of the molded body is 1 g/cm3 or less thereof for floating on water.
According to the present invention, algae cultivating medium that can float on the seawater and fresh water can be manufactured in a large quantity.
In the present invention, the molding step can comprise the steps of charging the mixture into a mold to form a preparatory molded body, and disintegrating the preparatory molded body to fine molded bodies. In this case, curing of the preparatory molded body preceding the disintegrating step can be carried out up to a level appropriate to the disintegration. Further curing can be implemented after the disintegration. A large volume of molded body can be rapidly manufactured by this method since the charging the mixture into the mold one by one is not needed.
A high-speed blade mixer having agitating blades revolving at high speed in a mixing tank can be favorably used in the present invention since homogeneous mixing can be obtained in a short time. By using a tank having approximately cylindrical shape and by placing agitating blades at the bottom thereof, the agitation and mixing are carried out very efficiently. A blade type mixer is particularly preferable as the agitating blades in order to obtain rapid mixing.
The molding step of the present invention can comprise a process of molding a molded body by agitating the mixture while spraying liquid selected from the group consisting of water and an aqueous solution of a curing material to the mixture. Curing process after the molding step can enhance the strength of the molded body. According to the present method, a huge volume of granular molded bodies can be formed in a lump. This molding process can be carried out after the mixing process continuously using a high-speed blade mixer for both mixing and molding. Of course we can use one mixer for mixing and another mixer for molding, however, we can eliminate wastes of time, labor and loss of the mixture at the transfer process by using the same mixer.
The molding step of the present invention can comprise a step of extruding a molded body by transferring the mixture to a die. According to this molding step, the molded bodies of prescribed shape can be manufactured in a huge quantity with good productivity.
The extruding step in the present invention can use a double tube or jacketed tube die. Further, the step can comprise the steps of extruding the mixture by transferring the mixture between an inner wall of an outside tube and an outer wall of an inside tube of the double tube. The step can further comprise sealing both edges thereof by cutting to form a molded body having a porous outside material layer and an inside cavity portion thereof.
Here, the cavity portion means a closed cavity without an inlet and an outlet. Apparent specific gravity of the molded body can be made small enough advantageous for the algae cultivating medium for floating on water surface.
The step for molding the molded body having an inside cavity can comprise the step of providing a low water permeability layer compared with the porous outside material layer between the porous outside material layer and the inside cavity portion.
The step of providing the low water permeability layer can be conducted by extruding by charging the porous material between an outermost tube and an intermediate tube of a die constituted by a three-fold tube and low water permeability material between the intermediate tube and an innermost tube thereof, and thereafter compressing and sealing off both edges thereof.
The low water permeability layer can contain at least one low water permeability material selected from the group consisting of coal ashes, incineration ashes, montmorillonite, kaolinite, cement, water glass, lime, and gypsum.
By employing these materials, the surroundings of the cavity portion can be made airtight. The molded body having a closed cavity surrounded by the airtight low water permeability layer can be made water floatable without containing density decreasing material by adjusting apparent density of the molded body.
The molding step of the present invention can comprise a step of compressing the mixture for forming a molded body. According to this molding method, the molded body of prescribed shape can be manufactured in a large quantity with good productivity.
The inorganic material in the present invention can be at least one selected from the group consisting of coal ashes, incineration ashes, sands, crushed shells, and diatomite. Among these, the coal ashes and incineration ashes are particularly preferable because they are industrial wastes that are produced in a huge quantity and their reuse is eagerly required.
The inorganic material at least one selected from the group consisting of coal ashes, incineration ashes, sands and crushed shells and diatomite can favorably be controlled not to contain components that pollute environment such as heavy metals and poisonous organic materials. The inorganic material can be subjected to a treatment for reducing or eliminating a component that pollutes environment such as heavy metals and poisonous organic materials. The coal ashes which is consisting essentially of stable oxide silica and alumina, can be used by managing to be free from the environment pollution components. The incineration ashes also can be used, eliminating environment pollution components at the stage of segregated collection or after-treatment of incineration ashes.
The curing material in the present invention can be at least one kind selected from cement, water glass, lime and gypsum. The curing material in the present invention can solidify the molded body while curing. The curing material can contain algae cultivating nutrient, for instance, phosphate compound as its constituent component.
The algae cultivating nutriment in the present invention can be one that contains at least one kind selected from phosphorus, nitrogen and iron is preferable. Nutriments for cultivating algae can be supplied from the medium containing the nutrient.
The raw material in the present invention can comprise at least 5 parts by weight of the curing material, and not more than 20 parts by weight of the algae cultivating nutriment, relative to 100 parts by weight of the inorganic material.
When the amount of the curing material is 5 parts by weight or more, desirable hardness can be obtained. In addition, the favorable amount of the algae cultivating nutriment is 20 parts by weight or less, since the algae increasing rate does not saturate at the amount.
In the present invention, the raw material can further comprise a density decreasing material in order that the algae cultivating medium be water floatable. The density decreasing material in the present invention can be at least one selected from the group consisting of alumina powder, pearlite, shirasu, shirasu balloon, or granular pumice stone, and diatomite. The density decreasing material can favorably be contained 10 parts by weight or more for decreasing the specific gravity of the molded body small enough to be water floatable.
The high-speed blade mixer in the present invention can preferably have a mixing tank of which bottom portion is tilted towards an exhausting outlet thereof. Productivity of the mixing process can be improved since mixer tank with tilted bottom portion easily exhausts the mixture.
The curing step in the present invention can comprise the curing of the molded body under heating. The curing under heating can be preferably carried out at temperatures of 100xc2x0 C. or more. Waste heat from a thermal power plant or a waste incinerator can be preferably used as a heat source of the curing under heating. Then waste heat is effectively used and an additional heat source for curing is not required.
According to the method of manufacturing algae cultivating medium of the present invention in which primary raw material is inorganic material, the molded body medium that can be floated on water surface and can cultivate algae is manufactured in a large quantity in a short time and in low cost. The algae can be cultivated in a large quantity inexpensively by dispersing on the oceans or the like the cultivating medium produced by utilizing the industrial wastes such as coal ashes, incineration ashes or the like as the principal raw material. While eutrophication and pollution of the oceans or the like can be avoided, and reduction of CO2 in the atmosphere which contributes to the prevention of the global warming up can be obtained. Further, the cultivated algae can be used as raw material of useful products such as alcohol or the like which can be used as a substituting energy source of fossil fuels. Accordingly, the present invention largely contributes in solving the environment and energy problem that the human race will encounter in the future.